FIG. 1A shows a data storage device 2 (e.g., a disk drive or a solid state drive) comprising control circuitry 4 and a non-volatile memory 6, such as a disk or a flash memory. The non-volatile memory 6 comprises a plurality of memory segments referred to as physical data sectors. To facilitate defect mapping, the physical data sectors are accessed indirectly through logical block addresses (LBAs). In this manner, if a physical data sector degrades, the system/user data can be relocated to a spare data sector and the corresponding LBA(s) remapped to the spare data sector.
The non-volatile memory 6 comprises a predetermined number of usable physical data sectors and corresponding LBAs (i.e., there is a maximum LBA). The LBAs may be divided into a number of partitions, wherein each partition stores a file system (e.g., a n-bit FAT file system, or a NT File System) identifying system files and user files. A partition may be bootable meaning that it stores a bootable operating system (OS) such as Windows OS or Mac OS. When a computer system is initially powered on, a master boot record (MBR) is read from the data storage device (typically stored in the first logical data sector). The MBR identifies a partition table that stores a partition map for each partition of the data storage device as illustrated in FIG. 1B. The partition table typically includes up to four primary partition maps identifying up to four primary partitions, wherein a primary partition may be further subdivided into extended partitions as illustrated in FIG. 1C. Each partition map (primary and extended) identifies a starting LBA and ending LBA of the corresponding partition, a file system type field, and a flag indicating whether the partition is bootable as shown in FIG. 1D. When the computer system finds a bootable partition, it uses the file system type field to access the partition's file system in order to read and execute the OS files from the partition (i.e., boot the computer system).